Edge Deletion: Are You Doing More Harm Than Good?

By Mike Burk

In a column appearing in the March 2005 edition of DWM magazine, I discussed the topic of edge deletion on low-E glass. Those 14 years ago I wrote, “The debate regarding edge deletion of low-E coatings continues. The response to the edge deletion requirement question is often ‘yes you do’ and ‘no you don’t’ from the same source.” Since then, things have changed—including equipment and coatings. But the debates rage on. Due to recent advancements, for those manufacturers that have chosen to edge delete, it’s probably time to take another look at your processes,
ensuring that the action of removing the low-E coating around the perimeter of glass isn’t doing more harm than good. When set up correctly, and with proper maintenances, the latest automated systems deliver the most consistent edge deletion quality without damaging glass.

Hands Off

The thing to know about manual edge deletion (by hand) is that, when not performed properly and extremely carefully, it can cause a great deal of damage to glass. Simply put: Each time a lite of glass is handled, another opportunity for damage occurs.

The breakout operator lifts the glass from the breakout table and slides it into a groove on a slot sorting rack. As the glass is placed into the rack, the operator must be careful that the leading corner is not rocked into the slot, but instead slid into position. Rocking the lite into the slot often causes scratching of the low-E coating on the lite in the next slot. This action can create the swoosh-shaped scratch that we all know so well. The rack then rumbles to the manual edge deletion station where the lite is removed and placed on the edge deletion table. Damage often occurs as the lite is loaded onto the table. The operator then rolls the lite against the stops and activates the edge deletion motor.

If the lite is not completely in place and square to the deletion wheel, the coating removal will be inconsistent. The operator then rotates the glass 90 degrees and reactivates the deletion motor. Again, if the lite is not square against the stops, the deletion pattern will be incomplete, often with rounding at the corners. The glass is rotated and deleted twice more, each of which presents more opportunities for damage.

The Ins and Outs

During manual deletion, the glass should only be handled by the edges. If the operator touches or maneuvers the glass by contacting the low-E surface, scratches will be created that may not appear until the window is installed and viewed in sunlight. Also, if the operators are not wearing masks, spittle and spray from their mouths can leave marks and defects in the coating.
If the edge deletion wheel is worn, or misadjusted, it may not sufficiently delete the low-E coating and can damage the glass. The most susceptible parts include the corners where the deletion wheel passes twice.

Next, some facilities, reload the lite into another slot sorting rack for future production. This is an additional opportunity for edge damage and scratching. Alternatively, other production facilities load the glass directly from the deletion table onto the washer entry conveyor. This method reduces handling, but often causes the deletion operator to rush in order to maintain the production pace. Speeding up the deletion process results in poor deletion and rounded corners.

No matter what equipment or methodologies used, it’s imperative that deleted glass be thoroughly inspected to insure complete deletion without edge damage. The deleted area and edges should be viewed under proper lighting, and also by a conductivity check.

I would suggest that it’s time, again, to head out on to the production floor. Stand back and watch the entire edge deletion process. Better yet, take someone with you who is totally unfamiliar with it. Explain to that person why you edge delete, how you edge delete and ask them their opinions. In the end, the question is: Are you sure that the cure is not worse than the disease?

Mike Burk is the North American technical representative for Sparklike.

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